In recent trends for electronic equipment having smaller sizes and greater functionality, connection terminals for components are becoming more miniaturized. Thus, in the field of electronic applications, various types of circuit connection adhesives are often used to facilitate the connection of such terminals. For example, to connect an electrode of an electronic component, such as an IC chip, with an electrode of a circuit substrate, such as glass substrate, a method for connecting the electrodes formed on the electronic component and the circuit substrate with a conductive adhesive containing conductive fine grains is employed.
The conductive adhesive is an adhesive in the form of film or paste in which conductive fine grains are dispersed in an insulative resin composition such as epoxy resin. The conductive adhesive is applied between the connection subjects, heated, and pressurized to adhere the connection subjects. More specifically, the heating pressurization moves the resin in the adhesive so as to seal, for example, gaps between a projection electrode (or bump) formed on the surface of an electronic component and a wiring electrode such as ITO electrode formed on the surface of a circuit substrate. At the same time, some of the conductive fine grains bite into the opposing projection electrode and wiring electrode to establish electric connection.
Due to recent trends for higher integration, the pitch between adjacent electrodes is becoming increasingly narrower, and pitches are becoming finer. Thus, electrode connection conductive adhesive must use conductive fine grains having small grain diameters.
Accordingly, various types of classifying devices for classifying conductive fine grains have been disclosed. More specifically, there has been a proposal for a current type classifying device including a disperser for dispersing fed dry grains into a primary grain state and continuously discharging dispersed fluid, and a cyclone tower connected immediately after a discharge port of the dispersed powder arranged in the disperser (see e.g., patent document 1).
The cyclone tower includes a spiral type powder inlet portion having a barrel, which serves as a main body for the cyclone tower and has a generally vertical tubular shape, and a powder guide inner wall surface arranged on the upper surrounding of the barrel. The disperser blows dispersed powder in the horizontal direction into the powder inlet portion, which gradually guides the dispersed powder radially inwardly with the power guide inner wall surface so as to produce a winding flow proceeding toward the inner wall surface of the lower barrel. Further, the cyclone tower includes a primary air outlet tube used to discharge grains. The primary air outlet tube extends downward over a certain length along the radially central position of the barrel from the ceiling of the cyclone tower and has an open lower end. The cyclone tower also includes a storage tank, which is connected to the lower open end of the cyclone tower, to store coarse grains that fall from the open lower end. During classification, a blower connected to the primary air outlet tube by way of a filter for collecting fine grains is operated under a predetermined flow rate to generate a current that circulates from the inside of the barrel of the cyclone tower and through the primary air outlet tube. Then, in this state, a power feeder continuously feeds powder to the disperser, and dispersed grains enter the powder inlet portion of the cyclone tower at a predetermined flow rate. The current containing the grains entering the powder inlet portion forms a winding flow along the spiral inner wall surface of the powder inlet portion. The winding flow descends as it is guided in a manner winding along the entire circumference of the inner wall of the barrel. Air is discharged out of the barrel through the primary air outlet tube. The current winding along the inner wall of the barrel generates a rising current at the central portion of the barrel while descending in the conical barrel. Therefore, in the grains contained in the current that descends while winding in the barrel of the cyclone tower, the grains having a large diameter and a relatively large weight settles downward and falls into the coarse powder storage tank connected to the lower open end of the barrel in accordance with the balance between the transfer action received from the current and the centrifugal force resulting from the mass of the grains. The grains having a small diameter and a relatively small weight pass through a fine grain transfer tube via the primary air outlet tube and are transferred to a filter by the action of the transferring force of the current discharged out of the primary air outlet tube. With this structure, grains having a diameter of 10 μm or smaller are sufficiently classified for industrial use.    Patent document 1: Japanese Patent Publication No. 2580193